Electrolytic cell method for transfer of dispersed solids from one liquid electrolyte to another with suppression of transfer of dispersing liquid

ABSTRACT

Dispersed electrodepositable coating binder and other codispersed electrocoating components co-depositable therewith can be recovered from one liquid dispersion into another liquid dispersion, which may be more concentrated than the dispersion from which recovery is made, without transfer of liquid dispersing medium therebetween by supplying the two dispersions respectively to two compartments of an electrolytic cell, each compartment containing an electrode, where the compartments communicate through a freely and non-selectively permeable nonconductive separator effective for arresting turbulent transmission of liquid dispersions therethrough in the absence of hydraulic pressure difference across the separator and charging the electrodes from an external source of direct current emf to attract dispersed electrodepositable coating binder through the separator toward the electrode in the compartment containing the dispersion into which recovery of binder is desired. Simultaneous transfer of liquid dispersing medium from one dispersion into the other is prevented by controlling the hydraulic pressure difference across the porous separator to be effectively negligible. Electrodeposition of binder onto the electrode in the cell compartment containing the dispersion into which dispersed electrodepositable binder is recovered and toward which that binder is attracted can be prevented, if desired, by sufficiently vigorous agitation of the dispersion in immediate contact with that electrode.

United States Patent 1191 Gilchrist 1 1 .Fan. 28, 1975 41 ELECTROLYTICCELL METHOD FOR TRANSFER OF DISPERSED souos FROM NE LIQUID ELECTROLYTETo ANOTHER WITH SUPPRESSION OF TRANSFER OF DISPERSING LIQUID [75]Inventor: Allan B. E. Gilchrist, Westlake.

v Ohio 1 7'3 Assignee: SCM Corporation/Cleveland, Ohio 221 Filed: July24, 1,974 21 Appl. NOQ: 491,387

521 U.S. Cl 204/180 R 51 1m.C1 B0ld 13/02 581 Field of Search 204/180R,180 1?, 301,

[56] References Cited UNITED STATES PATENTS 892,188 6/1908 Schwerin204/180 R 1,022,523 4/1912 Whitney 204/180 R 1,986,920 1/1935 Cross204/180 RX 2,944.952 7/1960 McMinn, Jr. 204/180R 3,682,806

8/1972 Kinsella ct al. 204/181 Primary Examiner- -John H. Mack AssistantExaminerA. C. Prescott Attorney, Agent, or Firm-James B. Wilkensco-dispersed electrocoating components codepositable therewith can berecovered from one liquid dispersion into another liquid dispersion.which may be more concentrated than the dispersion from which recoveryis made. without transfer of liquid dispersing medium therebetwcen bysupplying the two dispersions respectively to two compartments of anelectrolytic cell, each compartment containing an electrode, where thecompartments communicate through a.freely'and non-selectively permeablenonconductive separator effective for arresting turbulent transmissionof liquid dispersions therethrough in the absence of hydraulic pressuredifference across the separator and charging the electrodes from anexternal source of direct current emf to attract dispersedelectrodepositable coating binder through the separator toward theelectrode in the compartment containing the dispersion into whichrecovery of binder is desired. Simultaneous transfer ofIliquiddispersing medium from one dispersion into the other is preventedby controlling the hydraulic pressure difference across theporous'separator to be effectively negligible. Electrodeposition ofbinder onto the electrode in the cell compartment containing thedispersion into which dispersed electrodepositable binder is recoveredand toward which that binder is attracted can be prevented, if desired,by sufficiently vigorous agitation of the dispersion in immediatecontact with that electrode.

10 Claims, 4 Drawing Figures,

PATENTEU JAN 2 81975 SHEET 2 OF 2 FIG.3

ELECTROLYTIC CELL METHOD FOR TRANSFER OF DISPERSED SOLIDS FROM ONELIQUID ELECTROLYTE TO ANOTHER WITI-I SUPPRESSION OF TRANSFER OFDISPERSING LIQUID BACKGROUND OF THE INVENTION The present inventionrelates to recovery of electrodepositable coating binder from a diluteliquid dispersion thereof (the term dispersion as used herein includes asolution) by treating such a dispersion in an electrolytic cellapparatus in which an electrical potential difference is established byan external source between the electrodes to electrically drivedispersed electrodepositable coating binder toward one of thoseelectrodes. More particularly, this invention is related to my earlierinvention of Process and Apparatus for Electric Cell Treatment ofLiquor, described in US. Pat. No. 3,748,244 the teachings of which areincorporated herein by reference, which deals with apparatus and methodfor complete or partial electrolytic separation of electrodepositablecomponents, such as resinous or polymeric electrocoating binders, fromother components of a liquid electrolyte while preventing an insulatingaccumulation of electrodeposited material on the electrode toward whichthe electrodepositable components are attracted by employing a porouselectrode and pumping the electrolyte rapidly therethrough, wherethecell apparatus also incorporates a grossly porous non-conductiveturbulence arrester to suppress turbulent inter-mixing of electrolytefrom the vicinity of the electrode toward which electrodepositablecomponents are attracted with electrolyte from the vicinityof theother,i.e, counter, electrode.

The present invention is also related to my earlier invention of Processfor Electrolytic Treatment of Liquors Using Pressure Cell With PorousElectrode Means, described in US. Pat. No. 3,679,565 the teachings ofwhich are incorporated herein by reference, which deals with complete orpartial separation of electrodepositable components, such as resinous orpolymeric electrocoating binders, from other components of a liquidelectrolyte by treatment in an electrolytic cell apparatus having atleast one porous electrode, where the electrodepositable material tendsto form a fluent electrodeposit upon one of the electrodes and thatfluent electrodeposit isprevented from accumulating on that electrode tothe extent of significantly increasing the internal electricalresistance of the cell by inducing sufficiently intense relative motionbetween the electrode upon which electrodeposition tends to occur andthe electrolyte in the immediate vicinity thereof by such means asrapidly spinning that electrode or employing as that electrode a porousconductor and pumping electrolyte therethrough or by heating 7 thatelectrode.

The present invention is more remotely related to my earlier inventionof Apparatus for the Treatment of Liquors Using Porous DepositionElectrodes, described in US. Pat. No. 3,798,150, which deals withpressure cell apparatus for the electrolytic treatment of conductiveliquors containing electrodepositable material, where the electrodes tobe polarized for attracting electrodepositable material are tubularporous electrodes, it being contemplated therein that the liquorcontaining electrodepositable material would be fed to the interior ofthe tubular electrodes and the electrodepositable materialelectrophoretically attracted to and electrodeposited upon such tubularelectrodes would be flushed through the walls of the porous electrodesby the flow of a small portion of the liquor therethrough into asurrounding collection zone by maintaining a small hydrostatic pressurehead within the tubes.

In this branch of the prior art, :recovered electrodepositable materialis collected in dispersed or solubilized form, but at a greaterconcentration, in a portion of the same liquid medium from which suchrecovery takes place. Thus, either a portion of that liquid medium isused to wash through a porous electrode material electrodepositedthereon and to resolubilize that material into a collection zoneotherwise separated from the feed stream of liquor to be treated or elsea substantial portion of the initial liquid medium in which theelectrodepositable material to be recovered is initially'dispersed isremoved from the cell in the vicinity of the counter electrode chargedto opposite polarity from the. electrode toward which electrodepositablematerial is electrophoretically attracted and upon which it tends toelectrodeposit and, since the liquor near the counter electrode willhave been depleted of electrodepositable material by electricallyinduced migration thereof toward the deposition electrode, the removalof such depleted liquor necessarily leaves behind a liquor enriched inelectrodepositable material (so long as removal thereof by netelectrodeposition or otherwise is substantially prevented) and thisenriched liquor can be collected from any convenient location in thecell such as by withdrawal through a porous deposition electrode. Theprocess of the present invention differs from this branch of the priorart in that electrodepositable material is transferred under theinfluence of an electrical potential established between two electrodesfrom one body of liquid in which it is dispersed to a second body ofliquid, in which it also appears in dispersed form, without thenecessity of any transfer of liquid medium between those two bodies ofliquid dispersion and, in fact, with provision being made to largelyprevent such transfer of more than an insignificant amount of liquidmedium, as will be hereinafter more particularly described.

A principal utility of the present invention is in connection with theelectrocoating art, in which a paint or other surface coating is appliedto an electrically conductive object temporarily'connected as anelectrode in an electrolytic cell apparatus and immersed in a body ofliqud electrocoating dispersion comprising a solvent or dispersingmedium and electrodepositable coating binder dispersed therein, byelectrically charging the object to be coated to a potential, relativeto a counter electrode also in contact with the dispersion, such thatdispersed binder will be electrically attracted toward andelectrodeposited upon the object to form a coating less conductive thanthe dispersion from which .it was deposited. The electrocoated, objectis typically removed from the liquid dispersion, disconnected from thesource of electrical potential, allowed to drain a portion of the liquiddispersion mechanically entrained by not electrodeposited thereon backinto the electrocoating cell and rinsed to remove the remainder of theliquid dispersion mechnically entrained but not electrodepositedthereon. The electrocoated object is then usually subjected toadditional coating and/or coating curing operations.

Liquid electrocoating dispersions often contain, in addition toelectrodepositable coating binder, ionizing solubilizer for the binder,pigment, surfactant, curing accelerator, anti-foamer, fungicide andother components commonly found in organic coatings and paints. Many ofsuch additional components will electrodeposit together withelectrodepositing binder to form the insulating coating, but ordinarilynot in proportion to their concentration in the dispersion. The solventor dispersing medium is ordinarily water, but may be some other suitablemedium. The dispersed coating binder is ordinarily an organicpolymerwhich ioniz'es sufficiently in the liquid solvent or dispersion medium,usually with the assistance of an ionizing solubilizer, to be reasonablystable against flocculation or precipitation and to beelectrodepositable upon a suitably charged electrode, but may be anionizable low molecular weight material which will polymerize during orsubsequent to electrodeposition to form an adherent binder polymer forthe protective coating in its final form. The coating binder may bechosen from a broad range of polymer types on the basis of availability,cost, processability and the properties desired in the coating to beformed by the electrocoating process. A typical formulation for anodicdeposition would have a maleinized linseed oil binder with a morpholinesolubilizer in water. A typical formulation for cathodic depositionwould have an organic polymer with tertiary amino groups as binder andlactic acid as solubilizer and be dispersed in water.'

It is frequently desirable to recover electrodepositable material, andparticularly electrodepositable binder, from the rinse effluent of anelectrocoating operation so that the electrodepositable material can berecycled to the electrocoating cell and also so that the rinse water canbe either reused or discharged without contaminating the environment. Anumber of methods have been proposed and/or used for recoveringelectrodepositable material from electrocoating rinse water. The mostpromising of these previously known methods appear to beultra-filtration, reverse osmosis and electrolytic methods such as thosedescribed in my own patents referred to above. A drawback of theultrafiltration and reverse osmosis techniques is that a great quantityof water must be forced out of the dilute rinse effluent by pressuringit through a filter membrane impermeable, or at least preferentiallyless permeable, to dispersed electrodepositable material and it isdifficult to make such filters or membranes both strongly selective inpermeability and highly permeable to water or other dispersing medium.In contrast, the process of the present invention involves the transferof only a rela-' tively small amount of electrodepositable materialcon-- tained in the dilute electrocoating rinse effluent into a moreconcentrated dispersion where it can be reused without inordinate (oreven any) dilution of the electrocoating bath dispersion.

Another problem which arises in the electrocoating art is that asmaterial is electrodeposited onto the object being coated, and therebyremoved from the-system, solubilizer remains behind in theelectrocoating bath dispersion. If it is not to build up to large excessconcentrations therein, it must be either separately removed, forexample by absorption onto an ion exchange resin, or theelectrodepositable material added to replenish the bath must beformulated with only so much solubilizer as will be incidentally lostfrom the electrocoating operation by evaporation, carry-out in the rinseeffluent, etc. Removing excess solubilizer from portions ofelectrocoating bath dispersion involves an extra process step and mayproduce local instability of dispersion, while employingsolubilizerstarved replenishment formulations may lead to difficulty andnon-uniformity in redispersion upon addition to the electrocoating bath.The process of the present invention can be used to transfer excesssolubilizer out of the electrocoating bath dispersion into the rinseeffluent at the same time and in the same apparatus that theelectrode-positionable material is being transferred from the rinseeffluent into the electrocating bath dispersion and without concurrentlytransferring more than insignificant amounts of solvent or dispersingmedium.

SUMMARY OF THE INVENTION An object of the present invention is toprovide apparatus and method for transferring electrodepositable coatingbinder from one liquid dispersion thereof to a second liquid in whichthe transferred binder will re- 'main in dispersed andelectrodepositable form until electrodeposited.

Another object is to provide apparatus and method for such transfer ofelectrodepositable coating binder from a liquid dispersion in which itis relatively dilute into a liquid dispersion in which it is relativelyconcentrated.

Another object is to provide apparatus and method for such transferwhere substantial transfer of solvent or dispersing medium from thedilute liquid dispersion to the concentrated liquid dispersion isprevented.

A particular object is to provide apparatus and method for such transferof electrodepositable coating binder from electrocoating rinse effluentto a portion of electrocoating bath liquid electrolyte.

A further particular object is to provide apparatus and method for suchtransfer of electrodepositable coating binder from electrocating rinseeffluent into electrocoating bath liquid electrolyte whilesimultaneously transferring ionizing solubilizer for said binder fromthe electrocoating bath liquid electrolyte into the electrocoatingrinseeffluent.

In all of these objects it is contemplated that electrodepositablematerial in addition to the electrodepositable coating binder, such aspigment, etc., may be present and recovered simultaneously with theelectrodepositable coating binder.

These object are achieved according to the present invention byemploying an electrolytic cell divided in two half-cell compartments,each containing a half-cell electrode, by a separator which iselectrically nonconductive, freely and non-selectively permable throughat least a portion of its area to liquid dispersions containingelectrodepositable coating binder, and effective for arresting turbulenttransmission of liquid contents of either of the half-cell compartmentsto the other of the half-cell compartments in the'substantial absence ofhydraulic pressure difference across the permeable portion of theseparator while permitting hydraulic and electrical communication ofrespective liquid contents of the two half-cell compartments through theseparatonA liquid dispersion of electrodepositable coating binder fromwhich binder is to be recovered is supplied to one of the half-cellcompartments so as to make contact with the half-cell electrode thereofand with the permeable portion of the separator. A liquid into whichbinder is to be recovered is supplied to the other of the half-cellcompartments so as to make contact with the half-cell electrode thereofand with the permable portion of the separator. An electrical potentialdifference of polarity and magnitude effective to driveelectrodepositable coating binder from the liquid dispersion from whichit is to be recovered through the permeable portion of the separatorinto the liquid into which it is to be recovered is impressed upon thehalf-cell electrodes, thereby depleting the liquid dispersion from whichbinder is to be recovered and enriching the liquid into which the saidbinder is to be recovered with respect to electrodepositable coatingbinder concentration. Where it is desirable to prevent the transfer ofany substantial amount of solvent or dispersing medium from one liquidto the other, approximate hydraulic equilibrium is established betweenthe two liquids where they communicate through the permeable portion ofthe separator to substantially prevent hydraulic flow ofliquidtherethrough.

In a particularly useful embodiment of the method of the presentinvention, the liquid dispersion from which binder is to be recovered isrelatively dilute in binder concentration and the liquid dispersion intowhich binder is to be recovered is relatively concentrated in binder ofsubstantially the same composition as the binder to be recovered. Inanother particularly useful method embodiment, the dilute dispersionfrom which binder is to be recovered is rinse effluent from anelectrocoating process and the liquid into which binder is to berecovered is a portion of the electrocoating bath liquid electrolyte.

In any of its embodiments, it is contemplated that the method of thisinvention may involve the simultaneous recovery of otherelectrodepositable coating components simultaneously with recovery ofthe binder and also that other non-electrodepositable components may bepresent in the liquids supplied to the half-cell compartments. Wherecontinuous operation is desired, liquid inlet and outlet means areincorporated in each half-cell compartment. Where it is desired tosubstantially prevent transfer of solvent or dispersingmedium throughthe separator, means for establishing and maintaining approximatehydraulic equilibrium across the permeable portion of the separator areincorporated in the apparatus and used in the process to prevent suchtransfer.

An additional particular embodiment involves apparatus and methodgenerally as described above, but wherein the half-cell compartment intowhich binder is to be recovered is itself an electrocoating cell inwhich the electrodepositable coating binder may be electrodeposited upona removable object comprising the half-cell electrode thereof.Ordinarily in this embodiment a counter-electrode would also be presentin this half-cell compartment in addition to the counterelectrode in theother half-cell compartment from which binder is to be recovered. Inthis embodiment, no measures would be taken to prevent an insulatingaccumulation of electrodeposited coating binder upon the half-cellelectrode of the half-cell compartment into which binder is to berecovered.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a simple, open-topelectrolytic cell suitable for practicing the method of the presentinvention wherein hydraulic pressure difference across thepermeableseparator is controlled by overflow of liquid through weir outlets andwherein agitation, if desired, is induced by a motor-driven stirrer.

FIG. 2 shows a closed-top electrolytic cell adapted for continuousoperation wherein agitation of the liquid contents can be induced byrapid recirculation of those liquid contents though a venetian-blindelectrode and wherein hydraulic pressure difference across the porousseparator can be controlled by adjusting the relative rates atwhichliquid is supplied, recirculated, and withdrawn.

FIG. 3 shows an elevation cross-section of a cell in which recovery ofelectrodepositable binder is directly into an electrocoating tankwherein electrodeposition of binder onto electrode workpieces issimultaneously occurring and where the hydraulic pressure differenceacross the porous separator is controlled by means of an overflow weiroutlet on one side of the separator floating on liquid on the other sideof the separator.

FIG. 4 shows a plan cross-section of the cell of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1, the shell or body I ofthe cell holds the two bodies of liquid which are to be treated in thecell. The cell is divided by a non-selectively permeable separator 2into two half-cell compartments 3 and 4, each of which contains ahalf-cell electrode, respectively 5 and 6. The liquid dispersion fromwhich electrodepositable coating binder is to be recovered. is suppliedto compartment 3 and the liquid into which binder is to be recovered issupplied to compartment 4. Hydraulic pressure difference across theseparator can be substantially eliminated by supplying additionalamounts of the appropriate liquid to these respective half-cellcompartments 3 and d so as to maintain the liquid levels therein at theheight of the respective overflow weirs 7 and 8, which are fixed atequal height. The weirs discharge overflowed liquids through outlets 9and 10, respectively. When it is desired to prevent insulatingaccumulation of electrodeposited material on electrode 6, this may beaccomplished by agitation of the liquid in half-cell compartment 4 bymeans of the stirrer driven by a motor 101, the intensity of agitationrequired for this purpose being greater, the greater is the electricalpotential gradient in the immediate vicinity of electrode 6. Electrode 6is indicated as positively charged with respect to electrode 5, whichwould adapt this cell for recovery of anodic electrocoating materialfrom dispersion in the liquid introduced into halfcell compartment 3through separator 2 into the liquid introduced into half-cellcompartment 4. It should be understood that reversing the polarity ofthe electrodes so as to make electrode 6 negative with respect toelectrode 5 would adapt the cell for corresponding recovery of cathodicelectrocoating material. Whichever polarity is required may be producedby connecting the electrodes to a conventional external source of directcurrent. I

FIG. 2 shows a vertical cross-section of a closed cell particularlyadapted for continuous operation. The body 11 is divided bynon-selectively permeable separator 12 into two half-cell compartmentsl3 and I4 and electrodes 15 and I6 are'located respectively within thosecompartments. Electrode is a porous electrode constructed from metalturnings confined between two spaced metal screens or perforated metalcompositions can move freely therethrough without mechanical entrapment.Porous electrode is sealed around its periphery to the body 11 of thecell, or alternatively to an inward extension of liquid outlet 20, sothat a liquid dispersion of electrodepositable coating binder suppliedto half-cell compartment 13 through liquid inlet 19 must flow throughporous electrode 15 in order to reach liquid outlet 20. Electrode 16 inhalfcell compartment 14 is a venetian-blind style electrode comprising aspaced series of electrically interconnected metal slats such thatdispersed electrocoating material will pass freely through the spacesbetween the slats thereof. Liquid into which electrodepositable coatingbinder is to be recovered is introduced into half-cell compartment 14between electrode 16 and separator 12 by introducing it through liquidinlet 21, valve 22, and connecting inlet 23. Pump 25 causes liquid to bewithdrawn from compartment 14 through electrode 16 and into liquidoutlet 24 where it passes through pump 25 and a portion is recirculatedto compartment 14 by way of inlet 23 and a portion is removed throughvalve 26 and liquid outlet 27 therefrom. The rate of liquid flow throughelectrode 16 is made sufficiently high to prevent an insulatingaccumulation of electrodeposited material thereon by adjusting the rateof recirculation of liquid through outlet 24, pump 25 and inlet 23.Ordinarily this recirculating flow will be much greater than the inputand output flows through inlet 21 and outlet 27, respectively. Opentubes 17 and 18 set into the top of the cell in compartment 13 and 14,respectively, serve to vent any gases generated during operation of thecell and to detect any substantial hydraulic pressure difference acrossthe porous separator '12. If these tubes are transparent, the pressuredifference across the separator can be visually observed as a differencein the height of rise of liquid in the two tubes and corrective actionto equalize those pressures by adjusting the setting of outlet valves 26to affect the back pressure in half-cell compartment 14 or by adjustingthe setting of a similaroutlet valve (not shown) in the outlet lines 20to affect the back pressure in half-cell compartment 13. Automaticcontrol could be provided by instrumented optical detection of theliquid levels in tubes 17 and 18 or by detection of those heights byproviding suitable conventional electrical circuits to be closed oropened by virtue of the electrical conductivity of the liquiddispersions as they respectively rise to touch or fall to break contactwith suitable electrical contacts exposed within those tubes. The signalfrom any such automatic pressure difference detector can be utilized toautomatically actuate adjustment of outlet valves 26 and/or a similaroutlet valve in-outlet lines -20 from compartment 13, if such valves areprovided-with conventional solenoid or other actuators. Again, theelectrode 16 is shown as an anode and electrode 15 as a cathode,renderring the cell suitable for recovery of anodic electrocoatingbinder from dispersion in the liquid introduced into half-cellcompartment 13 by electrical migration through porous separator 12 intothe liquid introduced into half-cell compartment 14; reversal of thispolarity would render this cell suitable for correspondingly recoveringcathodic electrocoating binder. Direct current of the appropriatepolarity is supplied by connecting the electrodes to a conventionalexternal emf source.

FIG. 3 is a cross-section elevation and FIG. 4 a crosssection plan viewofa cell adapted for recovering electrodepositable binder from a liquiddispersion thereof directly into an electrocoating bath liquidelectrolyte dispersion in a cell where electrocoating of an object isproceeding simultaneously with the recovery of binder. The view of FIG.3 corresponds to section BB of FIG. 4 and the view of FIG. 4 correspondsto section AA FIG. 3. A liquid containing dispersed electrodepositablecoating binder is introduced into half-cell com partment 33 of cell 31through liquid inlet 40. Half-cell compartment 33 is divided from thereminder of this cell, identified as half-cell compartment 34, by avertical cylindrical separator 32, a lower portion of which isnon-selectively permeable to passage of dispersed electrocoatingmaterial. Compartment 33 also contains a solid electrode 35approximately concentric with the separator 32. Half-cell compartment 34is filled to a suitable level with a liquid electrolyte dispersion of anelectrodepositable coating binder and workpiece electrode 36 supportedby a conventional supporting member 41 and connected to an externalsource of direct current emf either through the supporting member 41 orby separate attachment of an electrical lead is immersed therein. Thehalf-cell electrode 35 and optional additional counterelectrodes 42 arecharged to opposite polarity from electrode 36 by connection to theexternal emf source. The polarities indicated, namely, the workpieceelectrode 36 as anode relative to the halfcell electrode 35, andoptional additional counterelectrodes 42, as cathode is suitable for usewith anodic electrocoating compositions. It should be understood,however, that by reversing the polarity of the electrodes, cathodicelectrocoating compositions can be treated in the present invention. Incontinuous operation, liquid in compartment 33 from whichelectrodepositable coating binder has been recovered by electricalmigration from dispersion therein through the permeable portion of theseparator 32 into the electrocoating bath liquid electrolyte dispersionin half-cell compartment 34 by overflow into the floating weir locatedin the upper region of compartment 33. From the weir, liquid drainsthrough vertically extensible liquid outlet 39. The overflow height ofweir 37 is maintained equal to the liquid level of the contents ofhalf-cell compartment 34 by attachment of the weir to flotation devices38, such as hollow metal spheres, which will float on the surface of theliquid in compartment 34, thereby insuring that substantial hydraulicpressure difference across the porous portion of the separator 32 willnot occur. Means conventional in the electrocoating art forreplenishing, filtering, cooling, agitating to maintain uniformity andfor moving workpieces into and out of the liquid dispersion in cellcompartment 34 would normally be provided, but are not shown.

The freely andnon-selectively permeable separator which divides the cellinto two half-cell compartments must be constructed of non-conductivematerial in order to avoid electrodeposition thereon. In oneparticularly simple and readily available form, the separator maycomprise a woven screen or cloth of glass or plastic thread of about 1millimeter in diameter having apertures in the weave of about 0.2 to 0.4millimeter. Several such screens can be placed in series, either incontact with each other or spaced apart, to form the porous separator.In another form the separator may comprise a rigid plastic sheetperforated by a plurality of holes of about 0.2 to 0.4 millimeters indiameter or a parallel series of such perforated rigid plastic sheetsspaced slightly apart from each other. It is important that theperforations or apertures in the separator be sufficiently large so thatthe largest components of the electrocoating composition to be treatedcan pass freely therethrough. For typical electrocoating compositions,apertures of 0.2 millimeters will be adequately large, but the treatmentof dispersions of many electrocoating compositions, andv especiallythose containing no pigments, considerably smaller apertures willsuffice. Permeable separators having perforations or aperturesconsiderably larger than 0.2 millimeters, and even considerably largerthan 0.4 millimeters, may be employed in the practice of the presentinvention so long as two conditions are satisfied.

The first condition is that the separator must substantially arrestturbulent transmission of the liquidcontents of either half-cellcompartment through the separator into the other half-cell compartmentin the absence of substantial hydraulic pressure difference across theseparator. For any given intensity of agitation of liquid cell'contents,more layers and/or greater thickness must be provided in the separatorstructure if large apertures therein are adopted. Similarly, if liquidcell contents are to be more intensely agitated, then either the maximumsatisfactory aperture size will be reduced or the minimum satisfactorynumber of layers or thickness of the permeable separator will beincreased. The second condition to be met in considering the maximumsize of apertures in the permeable separator is that although theapertures must be large enough to freely pass the largest dispersedcomponent of the electrocoating composition to be treated, nonetheless,there must be sufficient resistance to flow therethrough to permitdetection of hydrauylic pressure difference across the separator inorder that corrective action may be taken to substantially eliminatethat pressure difference and thereby to substantially prevent thehydraulic flow of liquid through the separator which would necessarilytake place if such hydraulic pressure difference were not otherwiserelieved. The more sensitive is the pressure difference detecting meansadopted, the smaller will be the required resistance to hydraulic flowthrough the porous separator that is required to activate it. Where abatchwise operation or a closed loop recirculating operation isinvolved, no such resistance to flow at all is required, since in suchcases liquid flow through the barrier can be readily detected bydirectly observing the volumes of the respective liquids present in thesystem on oppo- I continuous or intermittent additions and withdrawalsof materials from the system, some means for detecting the occurrence ofhydraulic flow through the separator by observing the hydraulic pressuredifference which produces that flow will be required in order to relievethat pressure difference and eliminate the corresponding liquid flowthrough the permeable separator.

Suitable means for detecting hydraulic pressure difference across theporous separator include, in appropriate contexts, provision foroverflow of liquids from the two half-cell compartments at equal fixedheights or for the overflow of liquid from one half-cell compartment ata height automatically adjusted to equal the height of liquid in theother half-cell compartment by flotation thereon or otherwise,instrumented detection of the absolute or relative heights of liquid inthe two half-cell compartments by means of optical devices, mechanicalflotation devices or by detection of the presence or absence ofelectrical conductivity as the electrically conductive dispersions riseor fall respectively through the level of the detection zone, but anyother means for detecting hydraulic pressure difference across theseparator or for detecting the liquid flow through the separatorresulting from such hydraulic pressure difference may be employed.Suitable means for preventing such liquid flow through the porousseparator as a result of hydraulic pressure difference across the porousseparator include, in appropriate contexts, manually controlled additionor withdrawal of appropriate liquid dispersion in one or both half-cellcompartments so as to reequalize the liquid levels therein, manual orautomatic adjustment of inlet and/or outlet valves controlling theinflow and/or outflow ofliquid dispersion from either or both ofthehalfcell compartments so as to equalize the back pressure in the twohalf-cell compartments; or direct overflow removal of excess liquiddispersion from either or both of the half-cell compartments, where theoverflow levels are either fixed or automatically adjusted so as toprovide equal liquid heights in both half-cell compartments as theappropriate liquid dispersion or dispersions are supplied to keep thecorresponding liquid level or levels at the overflow height. Other meansfor accomplishing the same function may of course may be employed.

The intensity of liquid agitation required to prevent an insulatingaccumulation of electrodeposited material on the electrode toward whichelectrodepositable material is electrically driven will. increase as therate at which such electrodeposition would take place in the absence ofagitation is increased. Thus, for any given compositions of the twoliquid dispersions to be treated in a given cell, the intensity ofagitation required to prevent insulating accumulation ofelectrodeposited material on the attracting electrode will increase asthe electrical potential difference between the two half-cell electrodesis increased, but will decrease as the temperature in the immediatevicinity of the attracting electrode is raised. A certain-amount ofelectrodeposition on the attracting electrode typically occurs as theoperation of a cell for the practice of the method of the presentinvention is commenced, but unless the net accumulation of suchelectrodepositable material is terminated before such insulatingaccumulation has proceeded to the extent that it significantly increasesthe electrical resistance of that electrode, the process will becomeincreasingly inefficient. If the potential difference across thehalf-cell electrode is maintained indefinitely, further net accumulationof electrodeposited binder upon the attracting electrode will ultimatelyterminate even in the absence of liquid agitation, but only when theelectrode resistance has substantially increased to the point where therate of deposition has been reduced to equal the rate ofresolubilization and the current flow in the cell has beencorrespondingly reduced. Where the cell is to be operated for recoveryof electrodepositable coating binder directly into an electrocoatingbath liquid electrolyte dispersion wherein electrocoating of workpieceelectrodes is simultaneously proceeding, the accumulation ofelectrodeposited material on the workpiece electrode ordinarily doescontinue to a condition'of substantial, but nottotal electricalinsulation thereof, but efficient continued operation of the cell ispermitted by removal of such insulated workpiece electrodes andreplacement thereof by fresh uninsulated workpiece electrodes. By aninsulating accumulation of electrodeposited material is meant a depositwhich appreciably increase the effective resistance of the electrodeupon which it is deposited.

The magnitude of the direct current electrical potential difference tobe impressed across the half-cell electrodes can vary over aconsiderable range depending somewhat upon the composition-of thedispersions to be treated, the shape and distance of separation of thehalf-cell electrodes, the intensity of fluid agitation that isavailable,-the rate of gas production at the half-cell electrodesthatcan be tolerated, the temperature, and other factors. Generally,potential differences across the half-cell electrodes which will producecurrent flow in the cell in the range from about 0.025 to aboutiLOamp/(decimeter) atthe surface of the electrode toward which dispersedelectrodepositable coating binder is attracted will be found mostsatisfactory. At significantly lower current densitiesthe rate ofrecovcry of binder would ordinarily be regarded as undesirably slow. Atsignificantly higher'current densities the rate of heating of the liquiddispersion in the cell and the rate of gas evolution from the electrodeswould ordinarily be regarded as presenting serious problems, but whereefficient cooling means for the liquid cell contents are available andwhere a high rate of gas evolution can be tolerated, then an electricalpotential which will, produce current densities substantially greaterthan 1.0 amp./(decimeter) may be used in the practice of the presentinvention. Where the process is being carried out by recoveringelectrodepositable binder directly into an electrocoating bath liquidelectrolyte dispersion by electrical attraction toward workpieceelectrodes being simultaneously electrocoated therefrom, themaximumtolerable current density will ordinarily be limited by theadverse effects'of'too high current density upon the quality of coatingbeing electrodeposited upon those workpiece electrodes. Furthermore, itis usually found that there isa threshold potential difference acrossthe half-cell electrodes of a few volts magnitude, below which norecovery of electrodepositable binders occurs and above which the rateof recovery of such binder increases continuously as the potentialdifferences is increased. The polarity of increases potential differenceis, of course, to be selected according to'the type ofelectrodepositable coating binder to be recovered, the attractingelectrode being positively charged for recovery of anodic electrocoatingbinders and negatively charged for recovery of cathodic electrocoatingbinders.

The shell or body of the cell should be constructed of non-conductivematerial, such as rigid plastic, vulcanized rubber, glass or ceramic. Itmay also be constructed of metal if a non-conductive lining of plastic,paint or other electrically insulating material is provided. Use of anon-conductive material of construction for the body of the cell isimportant for otherwise binder may electrodeposit in substantialquantities upon the inner surface of the cell body and the electricalmigration of dispersed binder will be correspondingly shortcircuited.

The'process of this invention may be used with liquid dispersioncontaining electrodepositable coating binder of any composition so longas it will migrate in the liquid dispersion in response to an electricalpotential gradient impressed therein. A great many suchelectrodepositable coating binders are known in the electrocoating art.Typical of binders suitable for deposition upon an anode is a maleinizedlinseed oil resin containing ionizable carboxylic acid groups. Typicalof binders suitable for electrodeposition upon a cathode is an organicpolymer containing tertiary amine groups, ionizable to form quaternaryammonium' groups. Usually such electrodepositable coating binders aredispersed in water, but other suitable liquid dispersing media can beused, and usually also an ionizing solubilizer is included to obtain andstabilize dispersion, including solution, of a greaterconcentration ofbinder than would otherwise be possible. Many such solubilizers arewell-known in the electrocoating art. Water soluble hydroxy amines aretypical of ionizing solubilizers used with anodic depositingelectrocoa'tingresins and soluble acids such lactic acid are typical ofionizing solubilizers used with cathodic depositing electrocoatingresins. Such soluble ionizing solubilizers, if present in thedispersions used in the process of the present invention, will migratein the opposite direction from the dispersed electrodepositable binderin response to the electric field produced by charging the electrodes.Pigments, extenders, fillers, curing agents,fungicides, leveling agents,etc., which comprise part of an electrocoating composition intended tobe deposited with the binder during electrocoating will also tend to berecovered together with the electrodepositable coating binder in theprocess of the present invention. While it would be possible to operatethis process so as to recover electrodepositable material from a moreconcentrated liquid dispersion thereof into a less concentrateddispersion liquid dispersion, this process will find its chief utilityin recovering such material from dilute dispersion into concentrateddispersion, and most particularly in recovering electrodepositablecoating binders from dilute rinse effluent from an electrocoatingoperation in to a portion of the electrocoating bath liquid elecyrolytedispersion.

EXAMPLE A closed electrolytic cell of the general type shown in FIG. 2was constructed of polymethylmethacrylate sheets using neoprene gasketsto seal the joints. The anode consisted of seven stainless steel plates4 inches X 1 inch spaced about 5% inch part in a tilted venetian blindarrangement and located in a 3 inches X 4 inches anode compartmentapproximately l k inches thick, and having a total volume of 300 cc. Thecathode consisted of 10 grams of stainless steel wool mat confinedbetween two stainless steel screens 3 inches X2 Va inches spaced if;inch apart and located in a cathode compartment which tapered from 3inches X 4 inches in cross-section to 2 A inches X 3 a in cross-sectionfrom the face of the porous separator to the face of the cathode. Theopposite face of the cathode opened into a liquid collection regionabout 2 54; inches X 3 Vi inches in cross-section by inch thick. Thecell was divided into anode compartment and cathode compartment by aporous separator consisting of 8 layers of 20 mesh per inchpolypropylene screen and three layers mesh per inch cotton gauze. Thecombined total volume of cathode compartment and cathode collectionregion was approximately 100 cc. The cathodeanode separation wasapproximately 1 16 inches. Inlet, outlet, and vent tube connections wereprovided for each half-cell as shown in FIG. 2.

A 20 percent resin solids solution was prepared from a phenolic modifiedmaleinized linseed oil electrodeposi-table resin of the sort describedin Examplel of my U.S. Pat. No. 3,230,162, incorporated herein byreference, having the following composition:

Resin 600. grams Triethylaminc 7.5 grams Diisopropanolamine 128. gramsButyl glycol 60. grams Deionized water 2204.5 grams This solution had ap I-I of 8.0 and a resistivity of outlet back to this reservoir.Similarly, 1290 cc. of the concentrated (8.9 percent) dispersion wasplaced in a reservoir connected by plastic tubing through a pump to theinlet of the anode compartment of the cell and plastic tubing wasconnected from the outlet of the anode compartment back to thisreservoir. A coil of copper tubing through which cooling water wascirculated was immersed in the liquid in this anode reservoir. The pumpswere adjusted to circulate 100 cc. per minute of the dilute dispersionthrough the cathode compartment and 1100 cc. per minute of theconcentrated dispersion through the anode compartment. The electrodeswere connected to a conventional direct current source of 400 volts andthe cell was run for 47 minutes to stabilize its operation. The currentflow was initially about 0.4 amps, but after about 7 minutes stabilizedat I approximately 1.0 amps, the decrease in the resistance indicatingthat some intermixing of the two dispersions had occurred while the cellwas initially being filled. A light deposit was observed to form on theanode plates, but this deposit did not continue to build up with time.After 47 minutes operation the dispersion circulating through thecathode compartment was analyzed to contain 1.8 percent resin solids andthe dispersion circulating through the anode compartment was analyzed tocontain 7.0 percent resin solids. At this time a new cathode reservoircontaining 560 cc. of the dilute (1.06 percent) dispersion was connectedto the cell, replacing the orginal cathode reservoir, withoutinterrupting the circulation of dilute dispersion to the cathodecompartment or the current flow in the cell, which continued atapproximately 1 amp. After another 20 minutes of operation, the dilutedispersion circulating through the cathode compartment was found tocontain only 0.6 percent resin solids and the cathode resservoir and itsfluid contents were again replaced-with a new reservoir containing 500cc. of, the dilute (1.06 percent) resin dispersion. Operation continuedfor another 20 minutes with approximately 1 amp current flowing in thecell. At this time both the cathode and anode reservoirs containing thedilute and concentrated dispersions of resin solids respectively weredisconnected from the cell and the flow of current was terminated. Theliquid in the cathode reservoir was analyzed to contain 0.3 percentresin solids and that in the anode reservoir 6.8 percent solids.Assuming that the contents of the small half-cell compartments in thisexperiment were of the same concentration as the dispersions in thecorresponding reservoirs being circulated through those compartments atany given time, a cumulative total of 7.5 grams of resin solids wasfound to have been transferred out of the two portions of the dilute(1.06 percent) dispersion circulated through the cathode chamber duringthe final two twenty minutes periods of operation. During the same time,a cummulative total of 15 cc. of total liquid volume was transferredfrom the dilute dispersions circulated through the cathode compartmentinto the concentrated dispersion circulated through the anodecompartment. The final analysis of the dispersion which had beencirculated through the anode compartment showed 6.8 percent resinsolids, with only a 15 cc. increase in total volume. While the directanalyses do not appear to positively show that the 7.5 grams of resinsolids transferred out of the dilute dispersions circulated through thecathode compartment were transferred into dispersion in the concentratedsolution which was circulated through the anode compartment, nonethelessthis must have occured since no additional deposit on the anode wasobserved nor was any separation of solids from any of the solutionsnoted. More importantly, no significant decrease in the current flow inthe cell had occurred, thereby negating any possibility that more than atrivial portion of the 7.5 gram of resin solids transferred out of thesolution circulated through the cathode compartment had electrodepositedupon the anode. The lack of direct detection of the transferred resinsolids in the anode compartment liquid dispersion is within the expectederror limit of those determinations, which were made by evaporation toconstant weight of 30 cc. aliquots in a 350 F. oven. Back pressure inthe two half-cell compartments was equalized by equalizing the height ofliquid rise in the two vent tubes by adjusting the discharge height ofthe flexible plastic outlet tubes from the respective half-cellcompartment.

What is claimed is:

1. In a process for recovering electrodepositable coating binder from adilute liquid dispersion thereof utilzing an electrolytic cell apparatusdivided into two half-cell compartments, each containing a half-cellelectrode, by a separator which is electrically nonconductive, freelyand non-selectively permeable through at least a portion of its area toliquid dispersions containing electrodepositable coating binder, andeffective for arresting turbulent transmission of liquid contents ofeither of the half-cell compartments to the other of the half-cellcompartments in the substantial absence of hydraulic pressure differenceacross the permeable portion of the separator while permitting hydraulicand electrical communication of respective liquid contents of the twohalf-cell compartment through the separator, the improvement whichcomprises:-

a. supplying to one of the half-cell compartments, to make contact withthe half-cell electrode thereof and with the permeable portion of theseparator, the dilute liquid dispersion of electrodepositable coatingbinder from which binder is to be recovered;

b. supplying to the other of the half-cell compartments; to make contactwith the half-cell electrode thereof and with the permeable portion ofthe separator, a concentrated liquid dispersion containing dispersedelectrodepositable coating binder of substantially the same compositionas the binder to be recovered and at a concentration greater than thebinder concentration in the dilute liquid dispersion;

c. establishing substantially hydraulic pressure equilbrium between thedilute and concentrated dispersions in the respective half-cellcompartments where those dispersions communicate through the separatorto substantially prevent hydraulic flow through the separator; and

d. impressing upon the half-cell electrodes in the respective half-cellcompartments, from an external emf source, an electrical potentialdifference of polarity and magnitude effective to driveelectrodepositable coating binder from the dilute liquid dispersionthrough the separator into the concentrated liquid dispersion, therebydepleting the diluteliquid dispersion in electrodepositable coatingbinder.

2. The process of claim 1 wherein the dilute and concentrated liquiddispersions of electrodepositable coating binder to be treated arecontinuously supplied to and corresponding depleted dilute dispersionand enriched concentrated dispersion produced thereby are continuouslywithdrawn from the respective half-cell compartments.

3. The process of claim 2 wherein the dilute liquid dispersion ofelectrodepositable coating binder is obtained from rinsing freshlyelectrocoated objects.

4. The process of claim 3 wherein the concentrated liquid dispersioncomprises a portion of the liquid electrolyte contents of anelectrodeposition cell for electrocoating articles. I

5. The process of claim 4 wherein the half-cell compartment to which theconcentrated liquid dispersion is the electrodepositable coating binderon a removable object comprising the half-cell electrode thereof.

6. The process of claim 5 wherein the half-cell compartment to which theconcentrated liquid dispersion is supplied additionally contains acounter electrode in contact with the concentrated liquid dispersionsupplied thereto and charged from an external emf source to anelectrical potential, relative to that impressed upon the half-cellelectrodes, such that electrodepositable coating binder is repelled fromthe counter electrode toward the half-cell electrode of the half-cellcompartment to which the concentrated liquid dispersion is supplied.

7. The process of claim 2 wherein the dilute and concentrated liquiddispersions of electrodepositable coating binder also each containionizing solubilizer for that binder.

8. The process of claim 7 wherein the ionizing solubilizer in theconcentrated liquid dispersion is driven by the electrical potentialdifference impressed upon the half-cell electrodes from the concentratedliquid dispersion through the separator into the dilute liquiddispersion, thereby depleting the concentrated liquid dispersion andenriching the dilute liquid dispersion in the ionizing solubilizer.

9. The process of claim 1 wherein an insulating accumulation ofelectrodeposited product of the electrodepositable coating binder uponthe half-cell electrode of the half-cell compartment to which theconcentrated liquid dispersion is supplied is substantially preventedand the coating binder -is substantially retained in dispersed andelectrodepositable condition in the enriched concentrated dispersionthereby produced.

10. The process of claim 9 wherein an insulating accumulation ofelectrodeposited product of the electrodepositable coating binder uponthe half-cell electrode of the half-cell compartment to which theconcentrated liquid dispersion is supplied is substantially prevented byinducing vigorous relative motion between the concentrated liquiddispersion in that half-cell compartment and the half-cell electrodethereof.

1. IN A PROCESS FOR RECOVERING ELECTRODEPOSITABLE COATING BINDER FROM ADILUTE LIQUID DISPERSION THEREOF UTILZING AN ELECTROLYTIC CELL APPARATUSDIVIDED INTO TWO HALF-CELL COMPARTMENTS, EACH CONTAINING A HALF-CELLELECTRODE, BY A SEPARATOR WHICH IS ELECTRICALLY NON-CONDUCTIVE, FREELYAND NONSELECTIVELY PERMEABLE THROUGH AT LEAST A PORTION OF ITS AREA TOLIQUID DISPERSIONS CONTAINING ELECTRODEPOSITABLE COATING BINDER, ANDEFFECTIVE FOR ARRESTING TURBULENT TRANSMISSION OF LIQUID CONTENTS OFEITHER OF THE HALF-CELL COMPARTMENTS TO THE OTHER OF THE HALF-CELLCOMPARTMENTS IN THE SUBSTANTIAL ABSENCE OF HYDRAULIC PRESSURE DIFFERENCEACROSS THE PERMEABLE PORTION OF THE SEPARATOR WHILE PERMITTING HYDRAULICAND ELECTRICAL COMMUNICATION OF RESPECTIVE LIQUID CONTENTS OF THE TWOHALFCELL COMPARTMENT THROUGH THE SEPARATOR, THE IMPROVEMENT WHICHCOMPRISES: A. SUPPLYING TO ONE OF THE HALF-CELL COMPARTMENTS, TO MAKECONTACT WITH THE HALF-CELL ELECTRODE THEREOF AND WITH THE PERMEABLEPORTION OF THE SEPARATOR, THE DILUTE LIQUID DISPERSION OFELECTRODEPOSITABLE COATING BINDER FROM WHICH BINDER IS TO BE RECOVERED;B. SUPPLYING TO THE OTHER OF THE HALF-CELL COMPARTMENTS, TO MAKE CONTACTWITH THE HALF-CELL ELECTRODE THEREOF AND WITH THE PERMEABLE PORTION OFTHE SEPARATOR, A CONCENTRATED LIQUID DISPERSION CONTAINING DISPERSEDELECTRODEPOSITABLE COATING BINDER OR SUBSTANTIALLY THE SAME COMPOSITIONAS THE BINDER TO BE RECOVERED AND AT A CONCENTRATION GREATER THAN THEBINDER CONCENTRATION IN THE DILUTE LIQUID DISPERSION; C. ESTABLISHINGSUBSTANTIALLY HYDRAULIC PRESSURE EQUILBRIUM BETWEEN THE DILUTE ANDCONCENTRATED DISPERSIONS IN THE RESPECTIVE HALF-CELL COMPARTMENTS WHERETHOSE DISPERSIONS COMMUNICATE THROUGH THE SEPARATOR; AND PREVENTHYDRAULIC FLOW THROUGH THE SEPARATOR; AND D. IMPRESSING UPON THEHALF-CELL ELECTRODES IN THE RESPECTIVE HALF-CELL COMPARTMENTS, FROM ANEXTERNAL EMF SOURCE, AN ELECTRICAL POTENTIAL DIFFERENCE OF POLARITY ANDMAGNITUDE EFFECTIVE TO DRIVE ELECTRODEPOSITABLE COATING BINDER FROM THEDILUTE LIQUID DISPERSION THROUGH THE SEPARATOR INTO THE CONCENTRATEDLIQUID DISPERSION, THEREBY DEPLETING THE DILUTE LIQUID DISPERSION INELECTRODEPOSITABLE COATING BINDER.
 2. The process of claim 1 wherein thedilute and concentrated liquid dispersions of electrodepositable coatingbinder to be treated are continuously supplied to and correspondingdepleted dilute dispersion and enriched concentrated dispersion producedthereby are continuously withdrawn from the respective half-cellcompartments.
 3. The process of claim 2 wherein the dilute liquiddispersion of electrodepositable coating binder is obtained from rinsingfreshly electrocoated objects.
 4. The process of claim 3 wherein theconcentrated liquid dispersion comprises a portion of the liquidelectrolyte contents of an electrodeposition cell for electrocoatingarticles.
 5. The process of claim 4 wherein the half-cell compartment towhich the concentrated liquid dispersion is supplied is operated as anelectrocoating cell to produce a coating comprising electrodepositedproduct of the electrodepositable coating binder on a removable objectcomprising the half-cell electrode thereof.
 6. The process of claim 5wherein the half-cell compartment to which the concentrated liquiddispersion is supplied additionally contains a counter electrode incontact with the concentrated liquid dispersion supplied thereto andcharged from an external emf source to an electrical potential, relativeto that impressed upon the half-cell electrodes, such thatelectrodepositable coating binder is repelled from the counter electrodetoward the half-cell electrode of the half-cell compartment to which theconcentrated liquid dispersion is supplied.
 7. The process of claim 2wherein the dilute and concentrated liquid dispersions ofelectrodepositable coating binder also each contain ionizing solubilizerfor that binder.
 8. The process of claim 7 wherein the ionizingsolubilizer in the concentrated liquid dispersion is driven by theelectrical potential difference impressed upon the half-cell electrodesfrom the concentrated liquid dispersion through the separator into thedilute liquid dispersion, thereby depleting the concentrated liquiddispersion and enriching the dilute liquid dispersion in the ionizingsolubilizer.
 9. The process of claim 1 wherein an insulatingaccumulation of electrodeposited product of the electrodepositablecoating binder upon the half-cell electrode of the half-cell compartmentto which the concentrated liquid dispersion is supplied is substantiallyprevented and the coating binder is substantially retained in dispersedand electrodepositable condition in the enriched concentrated dispersionthereby produced.
 10. The process of claim 9 wherein an insulatingaccumulation of electrodeposited product of the electrodepositablecoating binder upon the half-cell electrode of the half-cell compartmentto which the concentrated liquid dispersion is supplied is substantiallyprevented by inducing vigorous relative motion between the concentratedliquid dispersion in that half-cell compartment and the half-cellelectrode thereof.